Born in Wabbaseka, Arkansas, Cleaver's family moved to Phoenix and then to Los Angeles. As a teenager he became involved in petty crime, and in 1957 was convicted of assault with intent to murder. While in prison, he wrote a book of essays, Soul on Ice, which was influential in the black power movement and infamous for, among many things, his admission to raping several white women which he defended as "an insurrectionary act." He also admitted that he began his career as a rapist by "practicing on black girls in the ghetto." However, in Soul on Ice he simply states that his criminal actions have nothing to do with his views in the book, which is now considered a classic by many people.

Cleaver was released from prison in 1966, after which he joined the Oakland-based Black Panther Party and served as its Minister of Information (spokesperson).

He was a candidate for President in 1968 on the ticket of the Peace and Freedom Party. That same year, he was injured in a conflict between the Panthers and Oakland police. Charged with attempted murder, he jumped bail to flee to Algeria - where he was joined by Timothy Leary. Cleaver placed Leary under "revolutionary arrest" as a counter-revolutionary, although Leary was later released. Cleaver later left Algeria, and spent time in both Cuba, and France.

In 1975, Cleaver modeled anatomically fitted men's pants he designed featuring a "Cleaver sleeve" which was a penis sheath that was basically a sock protruding from the front of a pair of pants (see "Eldridge Cleaver Models his hot new pants" in Rolling Stone issue 197 dated October 9, 1975). The sleeve accommodated free movement and size changes of the enclosed male organ.